1. Field of the Invention.
This invention relates to a protective system for a refrigerant compressor. More particularly, the invention pertains to a digital logic circuit that disengages the compressor from the engine of an automobile when the quantity of refrigerant is insufficient.
2. Description of the Prior Art.
Automotive air conditioning systems have oil or other lubricant mixed with the refrigerant that circulates among the condenser, evaporator and compressor. If the refrigerant charge within the air conditioning system decreases, perhaps due to leakage, to an insufficient quantity the passenger compartment may not be adequately cooled and the compressor may be supplied with an insufficient amount of lubricant.
To avoid damage to the compressor resulting from an insufficient supply of lubricant and to avoid the recurring incidence of an inadequately cooled passenger compartment, the air conditioning system of an automobile should have provision for sensing a low charge of refrigerant and means for warning the vehicle operator of this condition. Further, the system should include a device that automatically disengages the driving connection between the engine and the compressor when the low charge condition exists.
Canter, U.S. Pat. No. 3,765,191 discusses a compressor protector which deactivates the compressor when the refrigerant charge level decreases below the quantity needed for cooling and lubrication. The electrical circuit for producing this result includes a heat biased relay, a battery, a fuse and a normally open switch. When the switch closes in response to high refrigerant temperature or low refrigerant pressure, the relay closes a circuit having a short time delay, which causes the fuse to open and deenergize the magnetic clutch. This renders the compressor inoperative until the fuse is replaced and more refrigerant is added to the system.
Basset, U.S. Pat. No. 3,686,892 teaches the use of a resistant wire heater located adjacent a fuse in an electrical circuit that supplies power through a normally open switch to a magnetic clutch that transmits drive from the engine to the compressor. The switch includes a refrigerant-filled bellows that expands in response to a predetermined refrigerant temperature in the compressor inlet to close the switch. When the switch closes, the wire heater is energized and after a time delay the fuse opens to de-energize the magnetic clutch, thus disconnecting the compressor from the engine.
Young, U.S. Pat. No. 3,631,685 includes a temperature responsive switch and a pressure responsive switch in an electrical circuit that operates to supply power to the compressor. If the power supply to the compressor is interrupted, a main switch opens and de-energizes the motor. A solenoid in the circuit is unable to be de-energized to close the main switch until the discharge pressure of the compressor is reduced to a low starting torque value.
The prior art has, therefore, included the use of electrical switches that operate in response to certain parametric variations in the operation of the air conditioning system to disable the compressor from continued operation that may produce damage to the compressor or continuously unsatisfactory cooling. Generally, these devices open the electrical circuit that completes a driving connection between the vehicle engine and the compressor. When the circuit is opened, further reactivation of the compressor is prevented until operation of the system is corrected by the replacement of an electrical component whose failure has indicated the hazardous operating condition. Once the operating parameter of the air conditioning system is recognized as being beyond an acceptable value and likely to cause damage to the compressor, no further operation of the air conditioning system is possible. Therefore, if the transducer or pressure switch is itself defective, replacement must occur before further operation of the system is possible. In the prior art a single malfunction of the pressure switch or a single operation of the transducer that works to sense the operating parameter of interest will completely disable the air conditioning system until the defective component is replaced or the system is recharged with refrigerant.